In desktop computing, it is now common to use more than one display device. Traditionally, a user would have a computer with a single display device attached, but now it is possible to have more than one display device attached to the computer, which increases the usable display area for the worker. For example, International Patent Application Publication WO 2007/020408 discloses a display system which comprises a plurality of display devices, each displaying respectively an image, a data processing device connected to each display device and controlling the image displayed by each display device, and a user interface device connected to the data processing device. Connecting multiple display devices to a computer is a proven method for improving productivity.
The connection of an additional display device to a computer presents a number of problems. In general, a computer will be provided with only one video output such as a VGA-out connection. One method by which a second display device can be added to a computer is by physically adding an additional graphics card to the internal components of the computer. The additional graphics card will provide an additional video output which will allow the second display device to be connected to the computer. However, this solution is relatively expensive and is not suitable for many non-technical users of computers.
An alternative method of connecting the second display device is to connect the additional display device to a USB socket on the computer, as all modern computers are provided with multiple USB sockets. This provides a simple connection topology, but requires additional hardware and software to be present, as in general, USB has a bandwidth that makes the provision of a good quality video output a non-trivial task. It is also desirable that any additional hardware between the computer and the display device is kept as simple as possible. This means that when connecting an additional display device using a limited bandwidth technology such as USB, certain complex tasks can be difficult to achieve.
In particular, complexity in many modern operating systems can make it difficult to support additional display devices. An operating system can be deployed on a wide variety of end computers with very different hardware capabilities, so it is common for some features within the operating system to be optional or to have different alternatives designed to suit different computing hardware. For example, in Windows® operating systems, a number of different display modes are supported, depending upon the capability of the graphics processing unit that is available on the computer that is running the operating system. The lowest level is commonly referred to as a “basic mode video” and more complex modes are also supported.
Third parties who provide hardware and/or software that will provide display functionality must ensure that their display solutions will work with all of the display modes that are provided within such operating systems. In particular, it is not sufficient to provide a display solution that only works with the default mode (usually the most advanced), the solution must also work with basic mode video. An example of such a display solution is the provision of an additional monitor for a computer that can be connected to the computer via a USB socket rather than a conventional VGA socket, as discussed above. Such an additional monitor will consist of hardware connections and software controlling the additional monitor and these must work even if the computer is running basic mode video. Since the basic mode operates in certain restrictive ways with respect to the creation and transmission of display data within the operating system, it is essential that any third party display solutions are still able to fully function, even in light of these restrictions of the basic mode.